The accident occurred during the first flight since the experimental amateur-built airplane had been repaired from a previous accident. The pilot stated that after departure he performed two landings without incident. On the third landing attempt, the in-flight electrically adjustable propeller went into a low/flat pitch while the airplane was on an extended final approach. The pilot stated that the airplane lost forward thrust as a result of the flat propeller blade pitch and that he landed short of the turf runway. The airplane subsequently nosed over and came to rest inverted; the fuselage and empennage were substantially damaged. The pilot reported that there were no preimpact mechanical malfunctions or failures that would have precluded normal operation of the airplane. He stated that the flat propeller pitch may have been inadvertently set during flight when he mistakenly depressed the propeller pitch selector instead of the intended push-to-talk button. Both buttons were collocated on the control stick.